Elasticsearch executes requests by breaking the request down into stages
and handing those stages off to different thread pool executors. There
are different thread pool executors for a variety
of tasks within Elasticsearch. Thus, Elasticsearch needs the ability to
create a lot of threads. The maximum number of threads check ensures
that the Elasticsearch process has the rights to create enough threads
under normal use. This check is enforced only on Linux. If you are on
Linux, to pass the maximum number of threads check, you must configure
your system to allow the Elasticsearch process the ability to create at
least 2048 threads. This can be done via /etc/security/limits.conf
using the nproc setting (note that you might have to increase the
limits for the root user too).